The present invention relates to a computerized typesetting system and, in particular, to an apparatus for computerized correction of type characters in a digital typesetting system.
Digital typesetting systems in commercial use employ computers to retrieve digital representations of characters of selected typestyles and produce an output of characters of typeset quality. For example, U.S. Pat. No. 4,231,096 shows a digital typesetter processing system in which parameters defining the typestyle, point size, spacing, and placement of characters are entered, normalized characters are retrieved from stored digital representations, the spacing and position of the characters are calculated for a given line width, and output character contours are derived by applying the typesetting parameters to the normalized characters. There are also various systems for modifying the shape of characters, for example, by horizontal and vertical scaling, such as disclosed in U.S. Pat. No. 4,029,947. In character generating systems, computers are also used to alter the overall shape of characters or to vary the density or aspect ratio of characters according to user specifications.
However, digital typesetting systems heretofore have not had the capability to modify parts of a character that are placed next to those of an adjacent character in order to produce a sharper or more pleasing visual appearance of a block of text. That is, characters of a particular typestyle have certain elements, such as the width of horizontal bars, serifs, or the contours of the edges, which may have a negative visual impact when viewed in juxtaposition to the elements of an adjacent character. For conventional systems, only one representation of a given character is available, regardless of the adjacent character combinations in which the character can occur. Some relatively simple procedures are used for condensing, slanting, etc. a block of text. Procedures for altering the letter spacing between particular pairs or triplets of characters, called "kerning", are also known.
If modification of the fit or contour of the elements of adjacent characters is desired, it is carried out manually by a graphic artist who cuts and pastes the modifications from standard character specimens. Since this is a very time consuming process, such modifications are not used in high volume typesetting jobs. Manual correction also provides little flexibility for the graphic artist to experiment with the visual appearance of different degrees of character element correction.
For some frequent character combinations, such as "ff", "fl", "fi", "ffi" or "ffl", the problem is met by using "ligatures", i.e. sets of two or three characters designed as a unit to replace visually awkward combinations. However, the use of predesigned ligature sets is limited to the specific combinations of characters, point sizes, letter spacing, etc. for which they have been designed. If the original ligature for a given text size is simply enlarged to a bigger size, the spaces in between the letters may be too large for a tight appearance, so that it is sometimes necessary to redesign the ligatures for specified point sizes separately. Ligatures replace only 5 out of 676 combinations for lower case characters in an average font. There are many other awkward lower and upper case combinations which could be but are not conventionally corrected.